Pulp manufacture



Jan. 24, 1961 F. B. K. GREEN, 2,969,113

PULP MANUFACTURE Filed Dec. 18, 1957 s Sheets-Sheet 1 [I v INVENTOR IFrankB.K. reen BY )f ww ATTORNE F. B. K. GREEN Jan. 24, 1961 PULPMANUFACTURE 8 Sheets-Sheet 2 Filed D80. 18, 1957 ATTORNE Jan. 24, 1961Filed Dec. 18, 1957 I F. B. K. GREEN 2,969,113

PULP MANUFACTURE 8 Sheets-Sheet 5 N- INVENTOR MWMQ ATTORNE Jan. 24, 1961F. B. K. GREEN 2,969,113

PULP MANUFACTURE Filed Dec. 18, 1957 8 Sheets-Sheet 4 ll ll l l 1 I l Ill m On (Q (Q s a Q INVENTOR ran 1: E. K reen,

ATTORNE Jan. 24, 1961 F. B. K. GREEN 2,969,] 13 PULP MANUFACTURE FiledDec. 18, 1957 8 Sheets-Sheet 5 1:1 17. T151. 15. go

250 INVENTOR Frank B. K. green Jan. 24, 1961 F. K. GREEN 2,969,113

PULP MANUFACTURE Filed Dec. 18, 1957 8 Sheets-Sheet 6 INVENTOR F- 13K.'e 9, mg: vj: em

Jan. 24, 1961 F. B. K. GREEN 2,959,113

PULP MANUFACTURE Filed Dec. 18, 1957 s Sheets-Sheet 7' Li J52 75 #90INVENTOR Frcg zk BK. green,

ATTORNE Jan. 24, 1961 F. B. K. GREEN ,9 1

PULP MANUFACTURE Filed. Dec. 18, 1957 8 Sheets-Sheet 8 n 6 N5 6w 5 m Qws: a, x M E "m V QNN. QNN K m m3 m MHIWIH n lfiwm W MP I a m E I 3N 3wPULP MANUFACTURE Frank B. K. Green, Massapequa, N.Y., assignor toSprout, Waldron & Company, Inc., Muncy, Pa., a corporation ofPennsylvania Filed Dec. 18, 1957, Ser. No. 703,588

9 Claims. 01. 162-237) This invention relates to the manufacture of pulpfrom wood or other fibrous material for making paper and the like and,more particularly, to methods and apparatus for cooking or digesting orsoftening the wood or other fibrous material to convert it into a pulpby a continuous operation.

As a result of technological and economic developments andconsiderations in the manufacture of paper, paper board and the like,from wood pulp or pulp of other fibrous materials, most of theoperations in a pulp and paper mill other than the pulp cooking anddigesting steps are carried on in a continuous fashion instead of in abatch-type manner. Accordingly, it may also be desired that the initialcooking and digesting steps wherein the ligneous and othernon-cellulosic encrustants or binding materials in wood are softened orremoved to render the Wood fibres desirably separable for preparation ofa pulp slurry also being carried out in a continuous manner forintegration with the other continuous processes of the mill.

According to this invention, then, methods and apparatus are providedfor continuously processing chips of wood through cooking and digestingsteps wherein the wood is subjected to the softening or cooking ordigesting action of chemical liquors at elevated temperatures andsubstantially super-atmospheric pressure for discharging the cooked woodinto subsequent pulp mill operations and apparatus. The apparatusembodying and for practicing this invention also is provided fordisposition in a pulp mill to occupy a minimum of space and yet providea plurality of parallel separately controllable lines of flow forconcurrently processing the same or different types of wood or other rawmaterials through a plurality of softening and cooking and digestingzones With an optimum efficiency in subjecting the raw material to aplurality of different cooking or digesting liquors and/or at aplurality of concentrations asthe cooking proceeds for achieving optimumcooking efliciency and minimal degradation of the cellulose fibresduring the cooking steps for optimum yield of finished product.

One object of this invention is. to provide apparatus of the characterdescribed for continuously cooking or digesting chips of wood or thelike at elevated tempera tures or pressures and having provision forsubjecting the chips to a plurality of different cooking or digestingconditions in a plurality of different cooking or digesting zones.

Another object of this invention is to provide apparatus of thecharacter described for continuously processing chips of wood or thelike at elevated temperatures and pressures through a plurality ofdifferent cooking or digesting zones and having provision for subjectingthe chips to a plurality of different cooking liquors or to cookingliquors of a plurality of different concentrations.

A further object of this invention is to provide apparatus of thecharacter described for continuously cooking or digesting chips of woodor the like for pulp manufacture by feeding the chipscontinuouslythrough a plu Patented Jan. 2%, 1961 rality of differentcooking or dig St ng Zones, and including m a s fer. arran ing th pparaus r c tinuo s flow p a ion to t vamin m of spac n h pulp mill.

A still further object of this invention is to provide, in continuousdigester apparatus of the character described, a plurality of parallelseparate lines of flow for continuous concurrent yet independentoperation substantially all contained in a single unit.

Still another object of this invention is to provide, in continuousdigester apparatus of the character described, means for arranging andsupporting and interconnecting the various components of the apparatusfor compensating for varying thermal expansion movement and strains andstresses within the apparatus and between the apparatus and otherequipment operating at different temperatures and pressures.

A still further object of this invention is to provide, in continuousdigester apparatus of the character described, a plurality of separatelycontrollable continuous flow arrangements for both chips of wood andcooking or digesting liquor in a unitary structure.

Other objects and advantages will be apparent from the followingdescription, the accompanying drawings, and the appended claims.

In the drawings:

Fig. 1 is aside elevation view of a continuous pulping system includingapparatus embodying and for practicing this invention;

Fig. 2 is an end elevation view of the system of Fig. 1 from the leftend thereof;

Fig. 3 is a side view partly in section and Withparts broken away ofadigester vesselem bodying and for pracdoing this invention;

.is a t pvi sim a to H s 3;

Fig.5 is a vertical a dal sectionpartly broken away on an enlarged scaleof digesting apparatus embodying and for practicing this invention alongthe line 5:75 of Fig. 2;

Fig. 6 is a partial transverse section along the line 66 of Fig. 3;

Fig. 7 is a partial transverse section along the line 777 of Fig. 3;

Fig. 8 is a partial transverse section along the line 8-8 of Fig. 3;

Fig. 9 is a partial transverse section along the line 99 of Fig. 5;

Fig. 10 is a vertical transverse section on an enlarged scale of ,oneofthe cooking liquor inlets of digesting apparatus embodying and forpracticing this invention along h lin .1010 of F g- Fig. 11 is a bottomview of the detail of Fig. 10;

Fig. 12 is a horizontal section on the line, 127.12 of Fig. 10;

Figs. 13 and 14 are top and side elevation views, respectively, of thecooking liquor piping arrangements of digesting apparatus embodying andfor practicing this invention;

Fig. 15 isa diagrammatic top view indicating the cooking liquor spraypatterns within the digesting vessel of Fig. 4;

Fig. 16 is a view from above of the inside bottom portion of thedigester of Fig. 4 with some of the internal structure removed forclarity;

Fig. 17 is a partial section onian enlarged scale along the line 1717 ofFig. 3;

Fig. 18 is a partial section along the line -1818 of Fig. 17; and

Fig. 19 is a partial section along the line 19-19 of Fig. 6.

Continuous digesting apparatus embodying and for practicing thisinvention, ,asvvill beunderstood, may be satisfactorily utilized in avariety of different systems or processes for cooking or digesting woodor other fibrous material in the production of pulp for the manufactureof paper, paper board, and the like. In order to achieve a more completeunderstanding of the structure and functioning and mode of operation ofapparatus according to this invention, it will be here described inconnection with a pulping system and process as disclosed in more detailin my copending application Serial No. 703,632, executed and filed oneven dates herewith.

Referring to the drawings, in which like characters of referencedesignate like parts throughout the several views thereof, a preferredpulping system including continuous digesting apparatus embodying andfor practicing this invention is indicated generally in side view andend view respectively in Figs. 1 and 2 as comprising feeding apparatusfor introducing chips of wood to be cooked into the digesting system andhaving driving means 11 operatively connected thereto, pre-steamingapparatus 12 for subjecting the chips of wood or other material to apreliminary steaming treatment or step and having its driving means 13operatively connected thereto, cooking or digesting apparatus 14 withits associated drive means 15 for subjecting the wood chips or othermaterial being cooked to the progressive cooking steps according to thisinvention, rotary valve means 16 with its associated drive means 17 fordelivering and metering chips from presteamer 12 into digester 14, anddischarge apparatus 13 with its associated drive 19 for discharging thecooked chips from digester 14 through blow line 20 for furtherprocessing and treatment to provide the character and quality of pulp orother fibrous material desired.

As indicated more particularly in the end view of Fig. 2, each of theaforementioned elements is preferably provided in pairs side by side(although the pair of digesting elements 14 as illustrated are bothenclosed within the same outer shell as hereinafter described) toprovide two independent parallel vertical processing lines or flows forhandling continuously and concurrently two lines of material beingprocessed. This preferential parallel arrangement provides extraoperational latitude and through-put control since, as describedhereafter, one kind of material or cooking chemicals may be processedthrough one line of flow while, at the same time, either the same or adiflerent material and cooking chemicals are processed through theparallel line of flow as may be required or desired by the capacityrequirements of the mill. Although only one of each of the duplicatedgeneral elements of this apparatus may be described in detail, it shouldbe understood that the corresponding member of the second parallel lineof flow is substantially a duplicate of the one described with, in someinstances, the drive means being mirror images, as indicated in Fig. 2.

The feeding apparatus 10 is preferably of the form shown in more detailin my above mentioned copending application and comprises a generallyhorizontal elongated barrel or casing having a feed opening orhopper-like inlet 26 in flow communication with an overhead supply ofchips to be cooked such as a conventional pulp mill chip bin (notshown). The chips are dropped by gravity into inlet 26 where a screwfeeder (not shown) rotatably driven by a motor 28 through a suitablereduction gear and drive 2931, urges the chips in a more or lesscompacted mass to the right of the drawing through barrel 25 so that thechips drop by gravity into and through the vertical outlet 35.

As indicated in Fig. l, the entire feeding apparatus and its drive arepreferably mounted on an elevated floor 46 above the remainder of theapparatus, with the chips being dropped by gravity through outlet 35 andinto subsequent apparatus through a hole in the floor. The chips dropfrom outlet 35 through a conduit 50 into the presteaming apparatus 12,and an expansion joint 5'1 or other expansion compensating means ispreferably interposed at some point between the outlet 35 of feedingapparatus It} and the inlet 52 of pre-steaming apparatus 12.

Pre-steaming apparatus 12, which is considered a preferred althoughoptional portion of the overall system and is described in more detailin my above mentioned copending application, comprises essentially acylindrical tube or casing 60 having therein a conventional screwconveyor or feeder (not shown) driven by a conventional drive 13. Thedirection of rotation and pitch of the screw flights of the conveyor aresuch as to urge chips introduced into the inlet 52 of pre-steamer 12 tothe left in the drawing to traverse substantially the entire length ofthe casing 60 and to drop by gravity out of the outlet 65 thereof.During passage through pre-steamer 12 the chips are subjected to theaction of super-atmospheric steam introduced into the interior of casing60 at one or more steam inlets indicated as 70, 71 and 72 to achieve thepreliminary steaming, saturation, and softening of the chips prior toactual contact with cooking or digesting chemicals. As will beunderstood, of course, for certain applications it may also be desiredto introduce some chemicals in addition to steam for a preliminarysoftening or preparatory step to condition the chips beter to receivethe principal or primary cooking actions in the subsequent digester 14.

As shown in Figs. 1 and 2, pre-steaming apparatus 12 is preferablysupported above the subsequent apparatus and suspended resiliently fromthe floor 46 as by hangers including springs 81 and depending tie rods83 engaging beams 84 on which rest casing 60. In this mannersubstantially the entire weight of pre-steaming apparatus 12 is carriedfrom above, rather than having to be supported on the remainder of theapparatus below pre-steamer 12, yet the height of pre-steamer 12 withrespect to the following apparatus is completely and automaticallyadjustable as required by the differential ther mal expansion movementsof the various elements of the whole system which may be subjected tovarying degrees of temperature at various times without unduly strainingthe conduit connections at inlet 52 and outlet 65 of presteamer 12. Alink or heated pipe tie rod 86 interconnects the end of casing 60opposite to outlet 65 with the corresponding end of digester 14 and isheated with steam to aid in maintaining substantial axial parallelismbetween 60 and 14 during heat expansion movements thereof.

From outlet 65 of pro-steamer 12 the treated chips drop by gravitythrough a conduit 35 into a rotary valve apparatus 16 which delivers andmeters chips into digester 14 and, since the cooking pressure indigester 1 1 is maintained at a level substantially above the pressurein presteamer 12, rotary valve apparatus 16, also is for preventing theescape of such higher pressure from digester 14 back into pre-stearner12. 7

Although the rotary valve apparatus 16 may satisfactorily be constructedin a number of dilferent ways to provide the desired functioning, apreferred construc tion is as shown in my copending application SerialNo. 703,590, executed and filed on even dates herewith. Rotary valve 16receives chips from pre-steamer 12 and drops them through chip outlet101 where they enter the digester 14 through chip inlet 102 thereof tobe sub jected to chemical cooking or digesting.

A preferred construction for digester 14 comprises an outersubstantially cylindrical shell within which are mounted a plurality oftroughs 121-124. In these troughs are screw conveyors 125128,respectively, rotatably mounted on shafts 129-132, respectively, journaled in the end plates 133 and 134 of shell 120 and rotatably drivenfrom drive means 15 mounted at one end of digester 14 and comprisingelectric motors 149 and 141 with corresponding reduction gear andchainand-sprocket drives 142-145 (see Figs. 5, 6, and 9).

The screw conveyor fights and direction of rotation are arranged toprovide for urging chips dropped into the upper troughs 121 and 122 fromthe chip inlets 10,2 axially toward the right in Figs. 1 and 5, whilethe lower screw conveyors 127 and 128 urge chips in the lower troughs123 and 124 axially to the left in Figs. 1 and 5. A plurality oflongitudinal splines 146 are preferably provided in troughs 121124 tocombat any tendency for the chips merely to rotate with the screws125-128 instead of traveling axially along the troughs.

As will be understood in the structure here illustrated, four troughsand screw conveyors are shown as a part of the system having the twoindependent parallel lines of flow mentioned above. Thus, troughs 121and 123 are in one line of flow whereas troughs 122 and 124 are in theseparate parallel line of flow and are operated inde pendently oftroughs 121 and 123 regardless of the fact that all four are containedwithin the single cylindrical casing 120 of digester 14. As with theforegoing elements of the apparatus embodying and for practicing thisinvention, only one set of troughs and screw conveyors 121, 123, 125,127 will be discussed in detail, the corresponding set of troughs andscrew conveyors being understood to be substantial duplicates.

As chips enter chip inlet 102 from rotary valve 16, they fall upontrough 121 and are conveyed axially therealong (to the right in Figs. 1and 5) by screw conveyor 125, which is preferably provided with acircular bathe or flange member 148 at the left or entrance and thereof.In progressing axially along trough 121 the chips are passed beneath aplurality of cooking ordigesting liquor inlets 15ti-154 from whichcooking or digesting liquor is sprayed onto the chips. Each of theseliquor inlets comprises a plurality of sprayheads 155 mounted on acircular cover 156 carried by inlet collars or flanges 157 in the top ofshell 120 of digester 14.

As indicated more particularly in Figs. -11, each cover 156 has adepending flange 1611 and a bottom plate 161 through which are mountedsprayheads 155. A transverse partition 162 divides the interior of cover156 into two separate chambers whereby the liquor. introduced throughpipe 163 may be separately con-trolled and, indeed, of completelydifferent composition than the liquor introduced through pipe 164. Aportion of the sprayheads (indicated as three in Figs. 11 and 12) arearranged with their outlet orifices 165 directed to spray liquor frompipe 163 toward one side of digester 14 to accommodate, for example,trough 121 while the remaining sprayheads 155 are directed to sprayliquor received from pipe 164 to the opposite side of the digester toaccommodate trough 122. That is, covers 156 are oriented in collars 157in casing 120 so that the partitions 1162 run axially of casing 120.

In this fashion, a liquor spray pattern is achieved as indicatedsomewhat diagrammatically in Fig. 15 with liquor being introduced to thechips in the upper digester at a plurality of points spaced axially ofthe digester and with, at each point, a separately controllable spraypattern directed independently to each of the two parallel lines offlow. As pointed out hereafter, the provision of a plurality of separateliquor inlets 150*154 has the advantage, according to this invention, ofsubjecting the chips being cooked or digested to cooking or digestingliquor of varying concentrations in various zones of the digester as thechips progress therethrough so that substantially raw chips entering thedigester at chip inlet 102 may first be subjected to highly concentratedcooking liquor at inlet 15%}, thereafter somewhat less concentratedcooking liquor through inlets 151 and 152, and, after the chips haveprogressed substantially through the upper trough of the digester, tosubstantially less concentrated cooking liquor through inlets 153 and154 whereby an optimum efficiency and use of cooking chemicals isachieved as well as a minimum of degradation of thecellulose as might beexperienced if chips in an almost cooked condition were subjectedto theharsh action of strong cooking .liquor. The internal pressure withincasing is maintained at the desired high level as herein described bythe admission of steam through steam inlet 166.

Since it is desired, according to this invention, to saturate the chipswith cooking liquor and thereafter subject them to high steampressurerather than to maintain the chips immersed in liquid phasecooking liquorthe bottoms of upper troughs 121 and 122 are perforated sothat liquor. sprayed on top of the chips in these troughs will slowlydrain through the chips as they are continuously being agitated by screwconveyors 125 and 126, will saturate the chips as completely as may be,and then any excess will drain off through the perforated trough sothat, atv various points along the travel of chips through the digester,the chips are being subjected to cooking liquor which they may soak up,but are not being agitated or maintained in a liquid pool of liquor.

The excess liquor draining from trough 121 is ultimately collected, asdescribed hereafter, at the bottom of digester 14 and removed throughliquor outlets and 171. Because of the arrangement of dam 172 andoverflow arrangement hereafter described in the bottom section of casing120 of digester 14, liquor draining from the left half of trough 121 iscollected through outlet 171) separately from liquor draining from theright half of trough 121, which is collected through outlet 171. Theseseparately collected batches of liquor, then, being of differentconcentrations since they are collected at different points in thecooking cycle, may be recirculated as indi cated in Fig. 14 forreapplication to chips moving through the digester. I

Thus, fresh and highly concentrated cooking liquor is introducedinitially through the first liquor inlet 15% and drains down to the leftside of dam 172 still substantially concentrated. This liquor'iscollected through outlet 1% and is recirculated by pump 175 driven bymotor 176 up through conduit 177 to be introduced at liquor inlets 151and 152 through pipe 163. After the chips have progressed approximatelyone-half the length of trough 121, however, a substantial cooking ordigesting effect has been obtained. Accordingly, the chips in the righthalf of trough 121 may be subjected to a substantially less concentratedcooking liquor, and this less concentrated liquor is withdrawn from apool on the right side of dam 172 through outlet 171 and recirculated bypump 180 driven by motor 181 throughconduit 182 to be sprayed on thechips in the right half of trough 121 through liquor in lets 153 and 154in substantially the same manner as above described.

The right-hand end 185 of trough 121 is spaced from the inside 186 ofend plate 1330f shell 120 of digester 14 so that, as the chips in trough121 reach the end 185 thereof, they drop by gravity onto lower trough123 along which they are conveyed back toward the left of the draw ingby screw conveyors 127 until they reach the left end 191 of trough 123which is spaced from the inside surface of end plate 134 of casing 120of digester 14, at which point the chips now completely cooked, drop bygravity through chip outlet 195 into the inlet 196 of dis chargerapparatus 18, described below.

The bottom of trough 123 is also perforated as with trough 121 so thatliquor continues to drain through the chips and out of the troughs. Itwill also be noted that trough 123 is positioned within casing 121 ofdigester 14 spaced above the bottom thereof to provide beneath trough123 a collecting pool of sump for collecting the liquor draining throughthe chips for recirculation, as above described. The aforementioned darn172 extends across this sump beneath trough 123 approximately at theaxial midpoint of the digester 14 whereby, as noted in Fig. 16, thecollecting sump beneath the lower trough is 7 Y divided intoapproximately two equal size pools for collecting the liquor forrecirculation.

Partition 200 extends axially along the centerline of casing 120 todivide the liquor collecting pool beneath the lower trough axially sothat there is a pool or sump for each of the parallel lines of flowmentioned above. An additional darn 201 is provided immediately adjacentchip outlet 195 to prevent the uncontrolled flow of liquor in the poolor sump out of chip outlet 195. The foregoing arrangements arediagrammed in Fig. 16 where the elements designated as 202204 representthe liquor and chip outlets for the other one of the parallel lines offlow mentioned above.

The heights of dams 172 and 201 are correlated with dam 201 being higherthan darn 172. Thus, as liquor collects in the left sump and the leveltherein rises, the cooking liquor will overflow dam 172 into theright-hand sump before the level of liquor behind dam 201 reaches aheight to overflow and escape out chip outlet 195. In this manner, themore highly concentrated liquor in the left half of the digesterautomatically and constantly replenishes the less concentrated liquor inthe right half of the digester, but diluting of the more highlyconcentrated liquor at the left with spent or weak liquor at the rightis avoided.

An overflow pipe 210 is also provided leading from an open overflow end211 at the right of dam 172 directly through darn 201 to dischargeliquor out of the end 212 of pipe 210 directly into chip outlet 195. Theheight of overflow 211 is lower than the dam 172 so that the level ofspent liquor to the right of dam 172 should build up sufliciently tooverflow that dam and dilute the more concentrated liquor. The level ofspent liquor to the right of dam 172 will build up and such liquor isautomatically drawn off through over-flow 211 and pipe 210 anddischarged directly out of inlet 195.

It will be noted that the arrangement described above as illustrative ofapparatus embodying and for practicing this invention results in acontinuous digester arrangement whereby the chips are subjected to threedistinct cooking zones in the digester 14. First, the raw chips in theleft half of trough 121 are subjected to the action of concentratedcooking liquor for the period of time it takes them to travel abouthalfway along trough 121. Second- 1y, a longer cooking zone wherein thechips are subjected to more dilute liquor is provided in the right halfof trough 121 and the right half of trough 123. A third and final zonewherein the chips are subjected only to vapor phase or steam pressurewithout the addition thereto of any cooking liquor may be provided inthe left portion of trough 123 immediately prior to the discharge of thechips through outlet 195. To this end, a transverse solid horizontalpartition 215 is provided beneath the left half of trough 121 andoverlying the entire width of trough 123 so that liquor draining out theperforated bottom of the left half of trough 121 flows across partition215 and down around the outside of trough 123 to the sump in casing 120therebelow but does not come in contact with the chips in the left halfof trough 123. This partition 215, however, extends for only about halfthe length of the digester so that the more dilute liquor draining fromthe perforated bottom of trough 121 at the right half thereof will draindirectly onto chips in the right half of trough 123.

It will be understood, of course, that, although the aforementionedthree distinct cooking Zones are described here, suitable arrangement ofa plurality of liquor outlets and liquor pool dams and recirculationpiping and pumps may be made to provide any number of distinct cookingzones and treatment effects as may be desired in practicing thisinvention, or, if desired, liquors of the same, instead of different,strength or concentration may be introduced and/or recirculatedthroughout. It should also be noted, as diagrammed in Fig. 16, thataxial baffles 220' are provided on the bottom of casing 120 and extendthroughout a substantial portion of the length of each half thereof andspaced from liquor outlets 170 and 171. The purpose of these battles isto force liquor in the separate pools beneath the lower troughs to flowor circulate around the baffles as it is withdrawn through liquoroutlets 170 and 171 to maintain solid matter in suspension in the liquorand avoid deposition of suspended solids in the sump portion at thebottom of casing 12% of digester 14.

Satisfactory structures for mounting and arranging the troughs 121-124and the various above mentioned dams, baflles, partitions, etc., withinthe casing 124) of digester 14 are indicated in somewhat more detail inFigs. 3-8 and 17-19, from which the screw conveyors and moving partshave been deleted for clarity. A T-bar 225 is provided substantiallyalong the axial centerline of casing 120, and axial side struts 226 and227 are arranged along the sides of casing substantially at the verticalmidpoint thereof as the major supporting and aligning elements for thetroughs 121-124. A vertical partition 200 divides casing 120 intosections axially below T-bar 225, While vertical partition 228 similarlydivides the upper half of casing 121) into two axial sections toseparate the two parallel lines of flow above mentioned.

At a plurality of points along the length of the casing 120 are spacedsupporting plates 230 vertically disposed resting on T-bar 225 andlongitudinal struts 226 and 227. The supporting plates 23ft are arrangedwith semi-circular cutouts for receiving and supporting the perforatedbottom portions of the upper troughs 121 and 122.

Also a plurality of supporting plates 231237 are spaced along the lengthof casing 120 vertically below the T-bar 225 and longitudinal struts226, and also have semicircular cutouts for receiving and supporting thebottom perforated portions of the lower troughs 123 and 124. Thestructure of these supporting plates, particularly in the bottom partthereof, vary somewhat according to their position along the length ofcasing 124 since it is plate 234, for example, which includes in thebottom portion thereof dam 172 previously referred to. That is, asindicated in Fig. 7, dam 172 is defined by the bottom edge 240 of acutout or opening 241 in plate 234. Also as noted in Figs. 68, overflowpipe 210 passes through the several supporting plates 231, 232, etc., inthe left part of casing 120.

In addition to resting in the semi-circular cutouts of the verticalsupporting plates, troughs 121124 are additionally supported at theupper edges thereof by being aflixed to longitudinal struts and/or T-oar225 as the case may be. Thus, bot-tom troughs 123 and 12 are affixed toT-bar 125 and longitudinal struts 22s and 227 are indicated in Fig. 6.The corresponding upper troughs 121122 are similarly affixed in theupper part of casing 120. That is, the upper edges of troughs 121 and122 which are inwardly disposed along the centerline of casing 120 areaflixed to a longitudinal strut 24-5 at the top of casing 120, while theupper outwardly disposed edges of troughs 121 and 122 are similarlyaflixed to longitudinal struts (not shown) adjacent the outer Wall ofcasing 120 at approximately the 10 oclock and 2 oelock positions on across-section thereof.

Since it may be desirable to construct the troughs, various internalbracing, and outer shell 12d of digester 14 from a variety of differenttypes of material (e.g., stainless steel and other steels), the extentof thermal expan sion movement may vary among the various parts. Forthis reason, provision is made in the described structure forcompensating for varying heat expansion movements therein. It has beenfound that the greatest amount of compensation for differentialexpansion movement is most satisfactorily applied axially of casing 121To end, the troughs and longitudinal struts are rigidly fixed to casing120 against axial movement at but one end thereo-fi.e., the left end inthe structure illustratedwith the other end arranged to permit somelimited axial movementwith respectato casing rl2tli Also, each-,,ofttroughfi 121--124.is provided in two'sections,,each "of whichlisapproximatelyone-halfzatti'ough long, As indicated in Fig. 19, a slidingexpansion joint'is-provided-where the troughs'meetandcompr-ises, asillustrated for trough 121, a .plate 25% weldedto the bottom 251 of theleft section of trough 12-1 so that the bottom-2520f the right sectionof trough 21 rests slidably on plate 25% thuspermitting a limited heatexpansion-movement compensationapproximately midway of theaxia lextentof trough 121. Aslo, as indieated'in Figs; 17 and -18,, .th,eupper edges of the troughs are aflixed to T'-bar 225 or the respectivelongi-tudinal struts 226, 227, 245-,-'etc., in a. manner permit tinglimited relative'axial movement Thatiis, at each point where the upperedges of anyof the troughs are to be bolted to any of the longitudinalstruts, an oval or oversize hole 255 is made in thetrough so-th-at, witha bolt 2S6 tightly and thread'ably; engagedzin the longitudinal-strut-(illustrated in Fig, 17 as.- 245), a liinited amount of axial relativemovement.ispermitted,between the trough and the strut as limited ordefined bythe length of hole 255;

As will be understood, the foregoing preferred structure provides,in'digester 14, thedesiredfeeding and supporting means for theperforated troughs, screw conveyors, etc., for moving thechips throug-hthe several cooking or digesting zones in digester, 1d andsuhjccting thechips to the desired cooking'or digesting iliquor.

The entire. digester 1 is preferably supported from below onsupports 225and 226* adequately above discharger 18. As will be noted, digestersupports ZZS-and 226 then carry substantially the entire-weight ofdigester 14 and its associated drive 15' as well as rotary valve 36 andits drive 17 as indicated in Figs. 1 'and2. Since presteamer 12 ispreferably supported fromabovegas before described, from resilienthangers affixed to the-floor above, this arrangement makes forsatisfactory;compensation for vertical thermally induced heat expansionmovements-of the various component partswithout'unduest'rain onthedigester 14 or its supports 225,226; The effect, inthis connection, ofexpansion joints 51 in conduit 56- and of tie rod 86 has alreadybeen'no-te'd. Alsov expansion joints 7 183 and 184 are provided in'-liquor conduits and outlets 170, 317i, 177, 182 etc., as desired: ornecessary;

Referring again to Figs. 1: and 2, in the system'illustrated, the chipsleave digester 14throughjchiproutlet,1:95 thereof after the cooking ordigestingis completed to the degree desired, and drop into discharger 18'throughinlet 1-96 thereof. Discharger 18 discharges-thecooked wood intoblow line 2%} for washing, refining, and/or other subsequent operationsto be performed on the pulp. As will be understood, a number ofdifferent blowing, discharging, or refining means may followdigester 14in the line of flow and receive the cooked chips therefrom, as is wellknown. A preferred form ofdischarger'for-the system as illustrated isshown and describedin, more detail in my copending application 703,589,executed and filed on even dates herewith, as comprising an outer casing260 within which is rotatably mounted; ahorizontal screw conveyor (notshown) driven by motor 261 through a suitable reduction gear and drivemeans 262, 263; As the cooked chips drop into casing 269) through inlet1%, the screw conveyor urges them'to the leftin- Fig. 1., and a seriesof blades on the conveyor (describedin more detail in my said copendingapplication) sweeps the mass of chips and whatever cooking or digestingliquor may be present past a discharge orifice'adjacent blow line 2i andcontrolled by blow valve 265. As the chips pass the orifice and entranceto blow line 20, the pressure in digester 14 (withwhich, of course,casing 26il-is in flow communication) blows the chipsthrough the orificeand out blow line'20.

Among the advantages of the foregoing apparatus will be noted enhancedoperational flexibility. For example, as noted, different kinds of wood(e.g.',- soft wood-such as p ineand hard Woodsuch as gum) may besimultaneously processedthrough the apparatus if it is desired that thepulp being made into paper should consist of an admixture ofdifferent'woods. Also it may be found that, for a certain type orquality of paper, part of the pulp furnished to the paper machine shouldconsist of pulp cooked to one particular yield and another part to adifferent yield. As will be apparent from the foregoing description,such a situation is readily handled by the system embodying and forpracticing this invention by controlling or adjusting theconcentrationof cooking liquor and/or the length of time required forthe chips to pass through the cooking or digesting apparatus. Similarly,it may be desired for a certain type or quality of paper that part ofthe pulp be sulfate or kraft pulp and another portion be manufactured bythe Well-known sulfite or neutral sulfite processes, and both kinds ofpulp can simultaneously be processed through the foregoing apparatus.Also, insuch situations, the various kinds or degrees of pulp arereadily mixed and metered by controlling relative speed through thedigester, and, if desired, may all be discharged therefrom through asinglecommon discharge apparatus.

Another important feature of apparatus embodying and for practicingthis-invention relates'to the enhanced uniformity of cooking which canbe achieved. Uniform cooking conditions for making pulp from wood dependupon a numberof variable factors, one ofthe most important of which isuniform heat distribution. Obviously the desired uniformheatdistribution is quite difiicult to achieve in conventional batch typepulp digesters because of their huge size, etc. Truly uniform conditionsare also diflicult to attain even in continuous digester apparatus wherethe arrangement consists of merely a cylindrical tube through whichthechips are urged by a screw-much like the structure of pre-steamer 12described abovesince, with such 'a tube substantially filled with chips,there is only a relatively narrow-surface or area near the top of thetube- Where the chips are directly exposed to steam, and a rather largeandpreponderate area around the sides of the tube for almost direct heattransfer from the chips through the tube walls.

In cooking or digesting apparatus according to this invention, bycontrast, steam can circulate freely around and among troughs 121124 formuch more uniform heating of the chips within casing 12% and only a veryminor portion of the chips in the digester is in contact with ordirectly exposed to the outer walls of casing 153%. Also the surface ofeach batch of chips directly exposed to either a vapor area or cookingiquor spray, in this apparatus, is much greater than a continuousdigester comprising. merely one ormore individual tubes as inpro-steamer 12i.e., no matter how full of chips are troughs 121-124,still the top surface of the mass of chips directly exposed to a vaporarea or to liquor spray is as wide as the greatest diameter of thetrough or screw conveyor. Thusv much more uniform cookingis achieved,both from the standpoint of uniform heat distribution as well asincreased chip area directly exposed to the cooking liquor spray.

This advantage, as will be understood, is obtained whether the apparatusis constructed as illustrated with a separate trough for each screwconveyor or whether, as may be desired, the apparatus is constructedwith a wider trough common to two or more screw conveyors, so long asthere is aplurality of troughs and screw conveyors within a common outercasing 129 so that only a very minor portion, if any, of the chipsdirectly contacts the outer casing, so that there are passages for vaporcirculation between and among the troughs, and so that as large aspossible a surface: area of: the massof chips is directly subjected tovapor and cooking, liquor spray.

It should alsobe noted .that uniform cooking of wood chips-to a uniformyield is rarely, if ever, obtained with pulping processes and apparatusheretofore used. As

11 will be understood, in conventional pulping processes and apparatusthe actual yield of the pulp produced isa composite of different yieldseven within the same batch. Such variations stem for a variety offactors. Thus, since the yield varies with the cooking temperature,nonuniform heat distribution within the digester produces variations inyield as between chips in the center of the chip mass, other chips incontact with the outer shell of the digester, and other chips directlysubjected to the admitted steam. Non-uniform liquor circulation isanother factor, as well as localized dilution of the cooking liquor bythe admitted steam and/or non-uniform liquor concentrations at variouspoints in the digester. Variations in the moisture content of the chipsentering the digester and variations in the density of the wood alsohave a non-uniform effect on the rate at which the cooking liquor willpenetrate into the chips and, consequently, the rate at which the chipswill be cooked. Another variation, and one of the most important, stemsfrom variations in the size of the chips themselves since smaller chipswill be penetrated more quickly by the cooking liquor than larger chipswith, of course, variations in the rate of cooking and the final yieldachieved.

If the chips are screened, however, prior to introducing them intohopper 26 of feeding mechanism whereby smaller chips are fed into one ofthe parallel lines of flow while larger chips are fed into the other. Inthis manner, a greater uniformity of yield and cooking rate is achievedby subjecting the smaller chips to less cooking than the larger chipseither by varying cooking liquor concentration or by varying thethrough-put rate at which the chips are fed through digester 14.

A similar advantage may be achieved by providing one or more additionalrotary valves 16 for introducing into digester 14 chips at one or moreadditional points spaced along the digester so that the largest chipsare introduced through chip inlet 102 and, thereafter, progressively,smaller chips are introduced at later positions along digester 14 sothat, although all the chips are mixed together as they leave chipoutlet 195, the smaller chips have been cooked for less time or at aless rate than the largest chips by virtue of being introduced todigester 14 at a later point in the travel of the chips through thedigester.

When the chips are introduced into digester 14 and kept separate thereinin different parallel lines of flow, the cooking time and rate iscontrolled by the speed of the conveying mechanism. When chips areintroduced into the same line of flow at different points therealong,the cooking time is controlled by the positioning of the point ofintroduction, and with this apparatus either or both methods of cookingrate control can satisfactorily be utilized so that, by contrast topulping processes heretofore known, wood chips, regardless of size canbe cooked under controllable conditions to the same yield, orcontrollably to different yields by controlling or adjusting or alteringthe cooking time (i.e., through-put rate and distance of travel),cooking liquor concentration, liquor-to-wood ratios, etc.

The same advantages can also be obtained with apparatus embodying andfor practicing this invention when it is desired simultaneously to cookdifferent kinds of wood,

such as hard wood and soft wood. By altering the type and/orconcentration of the cooking liquor in the two sides of the digester andadjusting the speed of the screw conveyors, the cooking or digesting ofpulp from hard woods on one side and soft wood on the other can besimultaneously accomplished and controlled for a substantially constantoutput of the two kinds of pulp in the desired relative ratio orproportions.

Particularly in installations where difierent sizes of chips areintroduced into digester 14 at different points therealong, the size ofthe perforations in the bottoms oftroughs 121-124 may advantageously beadjusted with respect to the chip size at various points. For example,

if chips which are retained by a one-half inch screen are introducedthrough chip inlet 102 with smaller chips being introduced at somesubsequent point along digester 14, the perforations in the left end oftrough 121 could be as large as /8" diameter thus permitting anincreased initial liquor-to-wood ratio, since the larger perforationswould promote drainage of excess liquor more readily. The perforationsin the right-hand end of trough 121 and/ or in trough 123, then, wouldbe somewhat smaller to retain whatever chip size was present in thoseportions of the troughs with, for certain conditions, the left half oftrough 123 having no perforations at all for the introduction thereintoof sawdust for an extremely short cooking period immediately prior todischarging the cooked wood from outlet 195.

As illustrative of a satisfactory system utilizing digesting apparatusembodying and for practicing this invention, satisfactory results areachieved with the illustrated apparatus in the manufacture of sulfate orkraft pulp from southern pine woods. For a rated capacity of 42 tons ofpulp per day for each of the two parallel lines of flow, the digester 14may satisfactorily be of a size approxi mately 8 ft. in diameter by 31ft. long with each of the four screw conveyors 125-128 having a diameterof approximately 34 in. and a pitch and speed of rotation to convey agiven batch of chips completely through digester 14 from chip inlet 102to chip outlet 195 thereof in 40 minutes when the level of chips in thetroughs is such that the conveyors are 90% full. As will be understood,the other elements of the illustrated system are constructed anddimensioned to correspond to such size and through-put capacity ofdigester 14. As previously noted, the cooking rate of total cooking timemay vary according to the size of the chips, etc., but is preferablymaintained within the range of from approximately 20 minutes toapproximately 40 minutes total dwell in the digester 14 for kraft orsulfate pulp adapted for the manufacture of kraft liner board. With suchan installation, conventional kraft cooking liquor (comprising, as iswell understood, sodium hydroxide and sodium sulfide) is supplied toliquor inlet at a concentration of approximately 320 to 400 poundsactive alkali (calculated as sodium oxide) per ton of pulp, supplied ata rate of approximately 32 to 40 gallons per minute, and superheatedsteam within the range of 350 to 375 F. is supplied through steam inlet166 to maintain the pressure within digester 14 at approximately 120 to170 p.s.i.

The cooking liquor collected, as above noted, in the sump at the bottomof casing 120 and withdrawn through liquor outlets 170 and 171 isrecirculated by pumps 175 and at approximately 200 to 400 gallons perminute through liquor inlets 151154, and spent liquor is withdrawnthrough overflow pipe 210 and discharged out chip outlet at the rate ofapproximately 30 to 40 gallons per minute under the satisfactoryconditions described. With such conditions, wood chips at the rate of 70tons per day are fed into each of the feeding mechanisms 10 to producethe aforementioned 42 tons of pulp per day out of each of the parallellines of flow and cooked to a yield within the range of 55% to 65%finished pulp product.

While the methods and forms of apparatus herein described constitute apreferred embodiment of the inven tion, it is to be understood that theinvention is not limited to these precise forms of apparatus, and thatchanges may be made therein without departing from the scope of theinvention as defined in the appended claims.

What is claimed is:

1. In a continuous digesting system for the manufacture of pulp fromwood chips and the like at elevated temperatures and pressures withcontinuous flow of said chips through said system, the combination whichcomprises a cooking and digesting vessel having an outer shell enclosinga plurality of troughs through which said chips are conveyed duringcooking and digesting thereof, means for continuously conveying saidchips through said troughs, means for introducing cooking and digestingliquor to said chips in said troughs for impregnation of said liquorinto said chips, means for withdrawing from said troughs excess liquorwhich does not impregnate said chips, means for collecting said liquorwithdrawn from said troughs for recirculation through said liquorintroducing means, and means for introducing steam under pressure intosaid outer shell for maintaining said elevated temperature and pressuretherein.

2. Continuous digester apparatus as recited in claim 1 in which at leastsome of said plurality of troughs are arranged directly one over theother, and in which said means for withdrawing excess liquor from saidtroughs includes perforations in at least a portion thereof.

3. Continuous digester apparatus as recited in claim 1 in which saidplurality of troughs are arranged one above another in parallel verticallines of flow whereby at least two parallel feeds of chips through saidvessel are separately conveyed through said troughs within said singleouter shell.

4. Continuous digester apparatus as recited in claim 1 in which saidmeans for introducing cooking and digester liquor includes sprayheads atthe top of said outer shell for spraying said liquor uniformly acrossthe upper surface of chips in at least one of said troughs and alsoincludes perforations in said trough through which liquor sprayed onto'said upper surface of said chips therein drains onto the upper surfaceof chips in another of said plurality of troughs.

5. Continuous digester apparatus as recited in claim 1 in which saidplurality of troughs undergoes a different extent of axial thermalexpansion movement than does said outer shell and in which saidplurality of troughs is anchored to said outer shell adjacent one endonly thereof for free thermal expansion movement axially of said shell,and having means for suspending said plurality of troughs within saidouter shell for accommodating and compensating for said differentextents of thermal expansion of said troughs and said shell.

6. In a continuous digesting system for the manufacture of pulp fromwood chips and the like at elevated temperatures and pressures withcontinuous flow of said chips through said system, the combination whichcomprises a cooking and digesting vessel having an outer shell enclosinga plurality of troughs through which said chips are conveyed duringcooking and digesting thereof, means for continuously conveying saidchips through said troughs, means for introducing cooking and digestingliquor to said chips in said troughs at a plurality of points therealongfor impregnation of said liquor into said chips, means for withdrawingfrom said troughs excess liquor which does not impregnate said chips,means for collecting said liquor withdrawn from said troughs in aplurality of pools within said outer shell for recirculation throughsaid liquor introducing means, said plurality of pools maintainingseparated liquor of diiferent concentrations for recirculation of liquorof different concentrations selectively through diiferent ones of saidplurality of liquor introducing means, and means for introducing steamunder pressure into said outer shell for maintaining said elevatedtemperature and pressure therein.

7. Continuous digester apparatus as recited in claim 6 in which saidmeans for collecting said liquor in a plurality of pools includes atransverse dam across the bottom portion of said outer shell formaintaining separation of liquor collected from one portion of saidplurality of troughs from liquor collected from other portions thereof,means for withdrawing liquor separately from said pools for separaterecirculation thereof, and overflow means associated with said dam forWithdrawing and wasting excess liquor accumulated in one of said poolsbefore the level in said pool rises sufficiently to overflow said damand mix with liquor in an adjacent said pool.

8. In a continuous digesting system for the manufacture of pulp fromwood chips and the like at elevated temperatures and pressures withcontinuous flow of said chips through said system, the combination whichcomprises a cooking and digesting vessel having an outer shell enclosinga plurality of troughs through which said chips are conveyed duringcooking and digesting thereof, means for continuously conveying saidchips through said troughs, means for introducing cooking and digestingliquor to said chips in said troughs at a plurality of points therealongfor impregnation of said liquor into said chips, means for withdrawingfrom said troughs excess liquor which does not impregnate said chips,means for collecting said liquor withdrawn from said troughs in aplurality of pools within said outer shell for recirculation throughsaid liquor introducing means, said plurality of pools maintainingseparated liquor of difierent concentrations for recirculation of liquorof different concentrations selectively through different ones of saidplurality of liquor introducing means, means for introducing steam underpressure into said outer shell for maintaining said elevated temperatureand pressure therein,and means for effecting flowing and agitation ofsaid liquor in said pools preventing settling therefrom of suspendedmatter therein.

9. In a continuous digesting system for the manufacture of pulp fromwood chips and the like at elevated temperatures and pressures withcontinuous flow of said chips through said system, the combination whichcomprises a cooking and digesting vessel having an outer shell enclosinga plurality of troughs through which said chips are conveyed duringcooking and digesting thereof, means for continuously conveying saidchips through said troughs, means for introducing cooking and digestingliquor to said chips in said troughs for impregnation of said liquorinto said chips, means for withdrawing from said troughs excess liquorwhich does not impregnate said chips, means for collecting said liquorwithdrawn from said troughs for recirculation through said liquorintroducing means, means for introducing steam under pressure into saidouter shell for maintaining said elevated temperature and pressuretherein, means for supporting said troughs within said outer shell forcompensating for heat expansion movement of said troughs and said shell,and supporting means including means for positioning said troughs withinsaid outer shell and spaced therefrom for free circulation of steamtherearound and spaced from said outer shell for maintaining uniformheat conditions within said troughs and notwithstanding heat lossesthrough said outer shell.

References Cited in the file of this patent UNITED STATES PATENTS

